"7 



ting the motions of the comets. Had such a doctrine of the laws 

 of motion been founded on facts or correct data, we should have 

 no difficulty in effecting a perpetual motion. The late proposed 

 aerial machine, although it did not possess a single element fit 

 for the purpose intended, was yet founded on the principle of 

 motion promulgated by the Newtonian doctrine, — to be pro- 

 jected into the air by one impulsive action, so as to acquire a 

 certain velocity, with which, it is said, it would be capable of 

 retaining itself at a certain elevation, and continue to describe 

 equal spaces in equal times. 



The following extract from a standard work on astronomy, 

 written by one of the first philosophers of the day, will at once 

 show on what foundation the orbitual motions of the ' Prin- 

 cipia ' are based, and how geometrical curves and the paths of 

 projectiles have been confounded. 



" All bodies with which we are acquainted, when raised into 

 the air and quietly abandoned, descend to the earth's surface in 

 lines perpendicular to it. They are therefore urged thereto by a 

 force or effort, which we term gravity, and whose tendency or 

 direction, as universal experience teaches, is towards the earth's 

 centre ; or rather, to speak strictly, with reference to its sphe- 

 roidal figure, perpendicular to the surface of still water. (See 

 Plate I.) But if we cast a body obliquely into the air, this ten- 

 dency, though not extinguished or diminished, is materially mo- 

 dified in its ultimate effect. The upward impetus we give the 

 stone is, it is true, after a time destroyed, and a downward one 

 communicated to it, which ultimately brings it to the surface, 

 where it is opposed in its further progress and brought to rest. 

 But all the while it has been continually deflected or bent aside 

 from its rectilinear progress, and made to describe a curved line 

 concave to the earth's centre, and having a highest point, vertex 

 or apogee, just as the moon has in its orbit, where the direction 

 of its motion is perpendicular to the radius. When the stone 

 which we fling obliquely upwards meets and is stopped in its 

 descent by the earth's surface, its motion is not towards the 

 centre, but inclined to the earth's radius at the same angle as 

 when it quitted our hand. As we are sure that, if not stopped by 

 the resistance of the earth, it would continue to descend, and 

 that obliquely, what presumption, we may ask, is there that it 



